Mechanical vibration system



April 1952 K. EHRAT ETAL MECHANICAL VIBRATION SYSTEM Filed Dec.

H l, ll J \XXX i n 1 H .mwwlmiiwww Patented Apr. 29, 1952 MECHANICAL VIBRATION SYSTEM Kurt Ehrat and Vladimir Milliquet, Baden, Switzerland, assignors to Patelhold Patentverwertungs- & Elektro-Holding A.-G., Glarus,

Switzerland Application December 10, 1945, Serial No. 634,040 In Switzerland December 13, 1944 4 Claims. 1

This invention relates generally to mechanical vibration systems and it has particular relation to systems in which the vibrations are electrically maintained.

Tuning forks or devices similar to tuning forks are used advantageously as frequency determining elements for the production of electrical oscillations in accordance with the feed back principle. These devices, known as tuning fork generators, possess a high degree of frequency constancy when they operate at a constant temperature and when any additional damping infiuence is avoided. Additional damping, that is by air friction and sound radiation, can be avoided by placing the vibration system in an evacuated casing.

Damping of appreciable magnitude also arises from the diversion of vibration energy through the base on which the tuning fork is mounted. The diversion of energy in this way may attain a particularly high degree which may cause a substantial variation in the frequency of the oscillations generated in the circuit controlled by the tuning fork. Another disadvantage of the transfer of the vibrations to the supporting base is that the mass and elasticity of the base have an effect upon the oscillation frequency which may cause an undesirable shift in the frequency.

In the prior art, it has been proposed to reduce the variation of the frequency of vibration by resiliently suspending the tuning fork. However, this construction has the disadvantage in many practical cases that the tuning fork does not form a solid unit with the base which carries the coils, contacts, magnetic circuit and other elements of its energizing system.

In many practical constructions a firmly joined and compact installation is required. The present invention makes possible such a construction of a tuning fork generator having a plurality of pairs of vibratory prongs symmetrically arranged and electromagnetically driven in such manner that the stresses at the base ends of the prongs are self-compensating about the axes of symmetry, whereby the tuning fork assembly may be rigidly secured to a base by fasteners located on an axis of symmetry without diverting any significant amount of energy to the base. As a result there is no increase in the damping of the vibrating fork due to the manner in which it is mounted.

The invention thus relates to a mechanical vibration system which is caused to oscillate or vibrate by electrical energy and which is characterized by a vibratory member having a point or points which are not subjected to translatory or rotary stresses, the vibrating system being rigidly fixed to a base at those :points. The excitation of the vibrating system may then be carried out in conventional manner by means of electrical or magnetic elements which are mounted on the base of the device.

Accordingly among the objects of the invention are: to provide for mounting a vibratory system or tuning fork in such manenr that the vibrations thereof are not transmitted to the base; and to so mount a vibratory system on a base that the frequency of oscillation remains substantially constant and independent of the characteristics of the base.

These and other objects and the advantages of the invention will be apparent from the following specification when taken with the accompanying drawing in which:

Fig. 1 is a schematic diagram of a mechanical vibrating system embodying the invention;

Figs. 2 and 3 are diagrams showing, in ex aggerated form, the vibratory movement of the tuning fork; and

Fig. 4 is a diagrammatic illustration of another embodiment of the invention.

The vibratory system of Fig. 1 comprises a multiple pronged tuning fork l of l-l-shape which is symmetrical about a longitudinal axis L and a transverse axis T. The tuning fork l is mounted upon a base 2 by screws or rivets 3 which pass through mounting holes 4 located along the longitudinal axis L of the tuning fork. The surface of the base is shaped or a spacer, not shown, is provided in known manner to leave a clearance between the prongs of the vibratory member and the base.

The four prongs of the vibratory member I are caused to vibrate by driving coils 5 on cores 6 which are located between the opposed prongs of each pair, the coils being energized with alternating current developed by an electronic tube 1. The feed back or control potential of the tube 1 is generated in the exciting coils 8 on cores 9 positioned adjacent and outside the ends of the respective prongs of the vibratory system. The driving coils 5 are in series with the energizing potential source, shown diagrammatically as a battery I 0, in the plate circuit of the tube, and the several coils 8 are connected in series with the grid biasing source II which is also shown diagrammatically as a battery. The energy output from the frequency-stabilized oscillator tube 1 may be through a transformer 12 having a primary winding in the plate circuit of the tube.

The driving coils 5 and exciting coils 8 are so connected in circuit with the tube i that the prongs of the double-ended tuning fork I Vibrate symmetricallywith respect to the longitudinal axis L. The flexing of the prongs of the vibratory member I is illustrated to an exaggerated scale in Figs. 2 and 3. It will be 'noted that the point of symmetry M, at the intersection of the longitudinal and transverse axes L, T, does not move during the vibration of the several prongs, and a consideration of the flexing of the prongs as they move between the alternate end positions of Figs. 2 and 3 will show that all points along the longitudinal and transverse axes are free from translatory and rotary forces.

As described above, the vibratory system I is secured to the base 2 by screws or rivets that pass through mounting holes 4 on the longitudinal axis of symmetry of the vibratory system. The portion of the system adjacent the mounting holes does not move and is not subjected to stresses tending to cause movement, and therefore the mounting screws or rivets 3 are not stressed and do not tend to transfer stresses to the base 2. In other words, the vibratory system does not transfer energy to the base 2 and is not damped by the base 2. It is not essential that the screws or rivets 3 pass through points which are entirely free from stress as substantial freedom from a damping action of the base 2 may be had when the mounting members pass through the vibratory system at points spaced from but adjacent an axis of symmetry of the vibratory system. For practical purposes, points located on or adjacent either axis of symmetry are sufficiently free from translatory or rotary movements or stresses to serve as mounting points.

The natural frequency of vibration and damping of the system can be regulated by varying the width k of the transverse bridge between the longitudinally alined pairs of prongs, for example by saw cuts 13 at the base of the prongs.

Other forms of multiple prong vibratory systems that have an unstressed point of symmetry M may be used, for example a system as shown schematically in Fig. 4 comprising four prongs l' which are angularly spaced by 90. The several prongs are vibrated between end positions a, b as shown in broken lines by driving coils, not shown. In this embodiment of the invention the point of symmetry M is vibrationfree and is suitable as a location for mounting the fork on the base plate. Of course additional 4 points near M can be considered as being substantially vibration free, particularly points located on the angle bi-sectors m and n.

The mechanical vibration system disclosed herein also can be used advantageously for the construction of electro-mechanical filters.

We claim:

l. A tuning fork generator comprising a vibratory member having a series of four prongs symmetrically disposed with respect to a point thereof, a supporting base, electromagnetic means on said base for setting adjacent prongs of said vibratory member into vibration towards and away from each other, whereby the stresses imposed upon said point of symmetry of the vibratory member by the flexing of alternatively arranged prongs neutralize each other and said point of symmetry is not subject to translatory and rotary stresses, and means extending at least approximately through said point of the vibratory member rigidly securing said vibratory member to said base.

2. A tuning fork generator as recited in claim 1 wherein said vibratory member is H-shaped.

3. A tuning fork generator as recited in claim 1 wherein the four prongs of said vibratory member are angularly spaced by 90.

4. A tuning fork generator comprising a multiple prong vibratory member having a pair of axes of symmetry at right angles to each other, a supporting base, electromagnetic means on said base for setting adjacent prongs of said vibratory member into vibration towards and away from each other, and means extending substantially through an axis of symmetry rigidly securing said member to said base.

KURT EHRAT. VLADIMIR MILLIQUET.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 45 Number Name Date 1,781,513 Holweck Nov. 11, 1930 1,838,502 Schluter Dec. 29, 1931 1,882,395 Pierce Oct. 11, 1932 1,909,414 Matte May 16, 1933 50 1,912,3 1.; Bulkingham May 30, 1933 2,008,263 Smith July 16, 1935 2,175,237 Young Oct. 10, 1939 2,247,960 Michaels July 1, 1941 2,259,131 Fleischer Oct. 14, 1941 

